There are many methods for liquid treatments to remove impurities, especially for water treatment. Typical treatment methods include distillation, reverse osmosis, electrodialysis, ion exchange, and freezing. Among them, the major methods utilized for large industrial scale applications include:
(1) Ion exchange: It uses ion exchange resins to treat liquid. The price of ion exchange resins is very high, and the process needs strong acids and alkali for resin regeneration, which produces secondary pollution. Moreover, the maintenance of the equipment is complicated.
(2) Reverse osmosis: This is the most commonly used industrial water purification method. It has advantages such as high desalination rate, simple process, etc. However, the macromolecule membranes are easily polluted and fouled by the organic substances, calcium and chlorine in water. It requires very restrictive pre-treatment system and the addition of several types of antioxidant and anti-scale inhibitor. These increase the complexity of the treatment system, and may cause troubles in system operation and maintenance.
(3) Electrodialysis: It is composed of the electrode plates, separation membrane, and ion exchange resins. Under the attraction forces of a DC electrical field, ions move through the membranes and are adsorbed on the ion exchange resins. However, the incorporated membranes are easily fouled, like in the reverse osmosis. Also, such treatment can only get rid of ions, and it has no effects on organic substances, colloid particles or other particles, or suspended solids. Moreover, the equipment consumes lots of energy due to the water electrolysis on the electrode plates.
A published patent CN2463054Y titled “Module for liquid treatment and purification” claims that the module has a function of self-regeneration and it addresses the problems of high energy consumption, and membrane fouling as well as the high system pressure. The module includes at least a pair of parallel power distribution panels, insulation baffles, electrode plates, power distribution components, and liquid inlet and outlet holes on the side plates. When a DC power is supplied on the positive and negative plates through the power distribution components and the power distribution plates, with the liquid to be processed passing through the positive and negative electrode plates, the impurity ions and charged particles in the liquids migrate to the positive and negative electrodes, and they are stored in the electric double layer on the electrode surface. Thus, the impurity ions and electrically charged particles and molecules in the liquid are removed from the processed liquid. When the positive and negative electrodes are shorted, the ions and charged particles stored in the electric double layer return to the liquid channel due to the disappearance of direct current electric field and the formation of the internal loop. The ions, molecules and particles are discharged with the washing liquid. The adsorbed organic matters on the electrodes can be decomposed when the electric field was applied. All the impurities are discharged from the electrodes at the regeneration stage and the electrodes can be re-utilized afterwards.
The structure of the liquid treatment modules described in CN2463054Y has the following shortcomings:
1) It can only handle a small amount of liquid. Because there are lots of power distribution panels, there are only limited space left to accommodate the electrode plates for liquid treatment. Hence the total handling capacity is limited;
2) The module structure is complex. Because the system requires multiple power distribution plates, each of which requires its own component, the reliability is reduced; and
3) Operating current is very large. The power distribution plates are connected to the DC power supply through their own distribution components. The large working current requires large power supply system, and thus, the manufacturing costs of the treatment devices increase.